The vegetative (or autonomous, independent of man's will) nervous system ensures the regulation of the functions of internal organs and glands of external secretion, the tone of blood vessels. It is represented by the central neurons located in the spinal cord and brain, ganglia (peripheral nerve cell cluster) and terminal synapses in which excitation is transferred to the cells innervated organ (tissue). Depending on the location of the centers in the brain and ganglia location, nature of the effect on internal organs and mediator released into synapses end, the autonomic nervous system is divided into parasympathetic (mediator usually acetylcholine) and sympathetic (mediator - noradrenaline). The main mediator and sympathetic and parasympathetic ganglion is acetylcholine. Embryogenetic neurons in the sympathetic ganglia are related clusters of chromaffin cells in the adrenal medulla and sinocarotid areas that receive cholinergic innervation. Medications, depending on the influence on synapses with noradrenaline or acetylcholine mediation, divided into the adrenergic and cholinergic agents.
The main mediator of the adrenergic system is norepinephrine. When released under the influence of nerve impulse in the synaptic cleft, it interacts with adrenergic receptors and then destroyed catechol-O-methyltransferase (COMT), or subjected to reuptake; in the cytoplasm of the nerve terminal norepinephrine deaminated monoamine oxidase (MAO). The chromaffin cells of the adrenal norepinephrine is methylated and turns into adrenaline - a hormone that affects mainly on metabolic processes, but retain the ability to excite the adrenergic system.
Based on the sensitivity of different chemical compounds emit two types of adrenergic receptors - alpha- and beta-adrenoceptors, each of which has at least two subtypes - alpha 1, and alfa2- beta1-, beta2 receptor subtypes. Alpha1-adrenergic receptors localized in the postsynaptic membrane (vessels, radial muscle of the iris, the gastrointestinal tract, smooth muscles of the bronchi distal departments), alpha2-adrenergic receptors - limit (CNS) and extrasynaptic in the vascular wall. Presynaptic alpha2-adrenergic receptors regulate the release of norepinephrine, participating in the system of negative feedback. In turn, the beta1-adrenergic receptors are located mainly in the heart, and beta2-adrenergic receptors - in the bronchi, blood vessels and the uterus. Presynaptic beta2-adrenergic receptors implementing positive feedback, stimulating the release of noradrenaline. Adrenergic agents can selectively act on different types of adrenergic receptors: excite them (agonists - agonists) or inhibit (or blockers adrenolytics - antagonists).
Main mediator of the parasympathetic nervous system is acetylcholine. Receptors sensitive to acetylcholine divided into m- (excited by muscarine) and n- (excited by low doses of nicotine). In turn, the m-cholinergic receptors depending on the localization divided into m1 (central nervous system, peripheral nervous system), m2 (the heart) and m3 (smooth muscles, exocrine glands). Nicotinic cholinergic receptors are divided into HN (neuronal) - CNS receptors, autonomic ganglia, the adrenal medulla and nM (muscle) - receptors striated muscle. Substances stimulating one or the other kind of cholinergic receptors, called holinomimetikami. They completely (m, n-cholinomimetics) or partially (m- or n-cholinomimetics) reproduce the effects of acetylcholine. Drugs that interfere with the interaction of acetylcholine receptors, called holinoblokatorami or anticholinergic.
In medical practice, adrenergic agents are used primarily in cardiovascular (hypo- and hypertension, coronary artery disease, arrhythmia, etc.), And allergic bronchopulmonary disorders, cholinergic drugs - in treating diseases associated with the violation of the tone of smooth muscles of internal organs (different types of colic or atony of the gastrointestinal tract and bladder, stomach ulcer, asthma, etc.).